The invention described in this disclosure was developed for broadcasting data via ATSC terrestrial digital television signals, but it applies equally well to broadcasting data via digital television in general, and in fact many aspects of it apply to broadcasting data via any point-to-multipoint digital broadcast medium.
There are three primary roles involved in broadcasting content which is not closely synchronized in time to accompanying, pre-recorded audio and/or video content:                Content Provider—an individual or enterprise providing content to be broadcast A content provider may be the original creator of the content, or may be simply an aggregator of content, or may be a combination of the two.        Content Recipient—an individual or enterprise receiving broadcast content A content recipient may be the end user of the content, or may be simply passing it on to the end user(s) via some communications medium, or may be a combination of the two.        Broadcaster—an individual or enterprise that provides the broadcast medium for getting the content from the content provider to the content recipient.        
A fourth role which may be very important in some situations is the Service Provider, an enterprise that contracts to manage the data broadcast activities of one or more of the other stakeholders.
There are many different possible payment models within this basic structure. Examples of some of the many possibilities include:                The content recipients may pay the content providers for the content, on either a subscription or pay-as-used basis, and the content providers may then pay the broadcaster for the use of the bandwidth.        The content may be licensed or sold to the broadcaster, and the broadcaster may get paid by the content recipients, on either a subscription or pay-as-used basis. (In this case the broadcaster may essentially be playing the role of both content provider and broadcaster, as far as data broadcasting is concerned.)        The content providers and/or the broadcaster may deliver the content to the content recipients free of charge, and get paid by advertisers for advertising embedded within the content in some way.        Some content providers and content recipients may be part of the same enterprise, so the providers simply pay the broadcaster for the use of the bandwidth to deliver the content to the recipients.        
Some data broadcasting applications may require that only those recipients who are entitled to receive the data can have access to it, and it must be kept confidential from all other parties. In some cases it must be kept confidential even from the broadcaster. In other cases keeping the content confidential from the broadcaster may not be permitted. Thus, encryption may be required, and it may need to be performed before or after the data reaches the broadcast station. Some data broadcasting applications may require compression to optimize the use of the bandwidth. If both compression and encryption are to be applied, typically compression must be applied first, since compression techniques seldom succeed in reducing the size of data that has already been encrypted. Some data broadcasting applications may require forward error correction. Data broadcasting applications may require many different scheduling schemes and delivery mechanisms for getting the content to a location where it can be inserted into the broadcast, and for actually inserting the content into the broadcast stream. Some situations may require that the content recipients be able to filter the data, and extract only a portion of the content to which they are entitled. Content may take the form of discrete blocks of data (e.g., files), or may take the form of continuous streams.